An apparatus and methods of this kind are known from U.S. Pat. No. 6,104,777 A.
The scatter produced in the object under examination (breast), the intensity of which may almost attain the order of magnitude of the direct, unscattered, image-producing primary radiation, results in image quality impairment by reducing the contrast, increasing the noise, and ultimately in respect of the image post-processing methods used for differentiating between various types of tissue in the images produced, in particular between glandular and fatty tissue in the breast. For differentiation in respect of two tissue types, techniques using a single energy spectrum, i.e. a single x-ray tube voltage, or the dual energy method using two voltage values are known in mammography. In both cases scatter compensation is required; with the dual energy method this is also because the amount of scatter is different in the two energy spectra.
To reduce scatter, mechanical measures have already been proposed. The use of slit collimators requires mechanical displacement of the slit collimators over the breast measuring field and is therefore time-consuming. Anti-scatter grids not only reduce the scatter, but also the imaging-producing primary radiation. Arguments in favor of dispensing with anti-scatter grids have been ongoing for years. For compression thicknesses of less than 4-5 cm, the dose could even be reduced or the SNR (=signal-to-noise ratio) increased if the grid is removed. On the other hand there are applications in which it is not technically possible to use a grid, e.g. in tomosynthesis.
A large number of computer correction methods have already been proposed. Methods of this kind are known e.g. from M. DARBOUX, J. M. DINTEN: Physical model based scatter correction in mammography. In: Proc. SPIE, Vol. 3032, 1997, pages 405 to 410 and from J. M. DINTEN and J. M. VOLLE: Physical model based restoration of mammographies. In. Proc. SPIE, Vol. 3336, 1998, pages 641 to 650 and in U.S. Pat. No. 6,104,777 A. These are convolution/deconvolution methods in which a scatter intensity distribution is approximated as a convolution of the primary radiation distribution using suitable convolution kernels. In the cited documents an analytical model is thus proposed with which the physical scatter process in the scatter object (breast) is explicitly computed as an integral transformation. However, this explicit analytical representation only describes first-order scatter, not multiple scatter. The intensity distribution of multiply scattered photons is assumed to be a spatially constant background over the detector surface and must be estimated from previously determined tables. The analytical model for calculating just the first-order scatter contribution requires 4-dimensional numerical integrations (3 space coordinates+energy spectrum) for each detector pixel, i.e. it is compute-intensive. Approximations are therefore required in order to reduce the computational complexity. Because of the high computational complexity it is proposed to perform the calculations in advance and tabulate the results.
In addition, W. KALENDER: Monte Carlo calculations of x-ray scatter data for diagnostic radiology. In: Phys. Med. Biol., 1981, Vol. 26, No. 5, pages 835 to 849 describes the use of Monte Carlo methods for simulating radiation propagation in radiography.